I used to cook mini versions of these biscuits for petit fours when I was head chef at the Castle Hotel in Taunton _ they really are that good. Even better, the mixture can be made raw, and frozen, then cut and baked when you want fresh biscuits.
225g (8oz) unsalted butter, softened
225g (8oz) caster sugar
170g tube Carnation Condensed Milk
350g (12oz) self raising flour, sifted
100g (3½oz) dark chocolate, chopped
100g (3½oz) hazelnuts, roasted and chopped
In a large bowl, cream the butter and sugar until pale. Stir in the condensed milk.
Mix in the flour and then work in the chocolate and the nuts. Divide the dough in half and place each half in a square of foil or cling film.
Roll into two thick sausage shapes. Chill well; this dough will keep quite happily in the refrigerator for a week or so.
When ready to bake, preheat the oven to 180°C, 350°F, Gas Mark 4.
Peel off the cling film or foil, cut off thick slices, and batch bake in the oven on trays lined with baking parchment for about 15 minutes or until golden brown at the edges, but still a little soft.